(Before I start this, my apologies if it seems to be a bit off subject, but I just thought that the parallels between Robin Wood and Holtz are interesting, and too numerous to be a mere accident.)
Holtz was the "Angel" equivalent of Robin Wood. Both men had suffered tragic losses at the hands of monsters, and both men dedicated their entire lives, not to fighting vampires specifically, but a quest to exact vengeance on the particular vampire responsible for their grief. Granted, Holtz was a vampire hunter before Angel killed his wife and children, but I got the feeling that he saw it as more a job or a duty, the way the average police officer sees his everyday routine. Once his "job" spilled over into his personal life, it became a personal vendetta, so much so that he, like Wood, actually formed an alliance of sorts, not with vampires, but with other evil creatures, Sahjahn (sp?) in Holtz's case and the First Evil in Wood's.
Driven by their lifelong obsessions, both men became blinded to the fact that the monsters responsible for their respective losses in effect no longer existed. In the end, both men wound up recruiting an ally with a connection to the objects of their obsessions, Giles on Wood's case and Wes in Holtz's, and ultimately, both men's attempts at vengeance resulted in ill feelings and loss of trust between friends, but no real success in their primary goal.
Short version, Holtz and Wood exploited the existing doubts of Wes and Giles in an unsuccessful attempt to kill Angel and Spike, resulting in at least temporarily destroying the bonds of trust and friendship between Wes and Angel, and Buffy and Giles. We might even take the parallels further by comparing Holtz's adoption of Connor, which resulted in his trying to kill Angel to Wood's support and encouragement of Faith when she betrayed Buffy, Holtz's death to Wood's momentary (seemingly) death on the bus after the battle on the hellmouth, and Connor's eventual acceptance of Angel as a loving father in Season 5 to Faith's referral to Wood as her "ex," but that would almost certainly be stretching the similarities to the limits, if not beyond.